preparation

Put oven rack in middle position and preheat oven to 400°F. Butter an 8-inch square glass or ceramic baking dish.

Stir together water, cornstarch, and 1/3 cup sugar in a small saucepan, then stir in rhubarb. Bring to a simmer, stirring constantly, then simmer, stirring occasionally, 3 minutes. Remove from heat and stir in strawberries.